1. Field
The present invention relates to a charging member, a process unit cartridge, and an image forming apparatus.
2. Description of the Related Art
Conventional electrophotographic image forming apparatus, such as copiers and printers, have mostly used a charger utilizing a corona discharge phenomenon, such as a scorotron. However, such chargers generate ozone and nitrogen oxides. Therefore, as a charger used for electrophotographic image forming apparatus, contact type chargers that an image carrier is charged by having a conductive charging member in direct contact with the image carrier have recently prevailed.
There is an increasing demand for a less resistant charging member for use in contact type chargers from the viewpoint of higher speed, higher image quality, and longer life. A charging member has been produced by a method in which a rubber material is shaped by pressing or injection molding, and is vulcanized, and then shaped molding is ground so as to obtain a desired shape and surface roughness. In recent years, the users' demand for cost reduction has boosted the use of lower cost processing techniques, including extrusion molding that achieves good productivity, omission of the grinding to reduce the number of the manufacturing steps, and vulcanization at atmospheric pressure that can be carried out with inexpensive equipment.
Methods for making a charging member include a molding method using a mold such as injection molding, a method in which an unvulcanized rubber is extruded into a tube, vulcanizing the extruded tube, and inserting a cylindrical metal shaft into the tube, and a method in which an extruder is equipped with a crosshead die, and an unvulcanized rubber covers a metal shaft, and then vulcanized. The latter two of the methods are becoming predominant, in which a rubber cylinder is obtained using an extruder that favors the reduction of processing cost.